The migration of the neural crest cells from the neural plate to the mandibular and maxillary processes constitutes the initial step in facial development. Excess vitamin A administered during crest cell migration inhibits the migration of these cells into the facial regions, thereby resulting in cleft palate and short snout. Recent experiments have shown that excess vitamin A stimulates the synthesis of a single glycopeptide in rat liver. Studies are currently in progress to determine the effect of excess vitamin A on glycopeptide synthesis in embryos at the time of neural crest cell migration. Proper secondary palate formation also involves the elevation of shelves from a vertical to horizontal position. Efforts will be made to develop a culture system which permits in vitro shelf elevation. Using this culture system in conjunction with drugs, it will be possible to directly test the importance of various cellular activities to shelf elevation. The final developmental event involved in secondary palate formation is shelf fusion. Previous work has shown that the epidermal growth factor (EGF) inhibits in vitro shelf adhesion. Studies are currently in progress to determine the effects of EGF on glycopeptide and glycoprotein synthesis in the palatal shelf epithelium.